Passing values between data tables - calculating values in document properties

I want to pass some calculated values from one data table to another to include in a new calculation, however there is no natural join between the tables. This would be most equivalent to referencing a single cell in another page in Excel.

Can I capture a calculated value from my initial table as a document property, and have it update as underlying parts of the calculated column change? I would then be able to insert that property into a calcualted column on the second datatable.

An example expression I'd want to capture as a Real number in a document property would be as follows:

Avg(
case
when [A]="${Input}" then [B]
else null
end
)

Any suggestions?